1. Field of the Invention
This invention relates to on-line measurement of machine cutting tool positions, particularly positions of lathe cutting tools such as drilling and boring tools.
2. Discussion of the Prior Art
A known such device is disclosed in U.S. Pat. No. 4,443,946. This known device includes an elongate stylus 14 attached to a member 12 that is movable in three dimensions relative to a fixed frame 11. The deflection of the free end 14c of the stylus 14 relative to the fixed member 11 is detected by a transducer 21 connected between the stylus 14 and said fixed member 11. This device is primarily used in the measurement of workpieces, which is why it is capable of measurement in three dimensions, i.e., in x, y and z directions. However, it should be noted that only two dimensions, e.g., x and z directions, are necessary for measuring lathe tooling.
To adapt this known device for tool gauging, it is necessary to attach special fixtures to it. One method for doing this is to permanently fix the probe such that it will not be in the way of normal machining operations. However, this is disadvantageous because the farther away the probe is from the datum position, the more subject it will be to thermal expansions due to minor temperature changes. Another method is to insert the probe in the spindle as if it were a collet. This procedure would greatly reduce the errors due to thermal growth, but it would also require removing the spindle tooling every time a cutting tool is gauged, which is not desirable.
To achieve a three-dimensional operation, the device disclosed in U.S. Pat. No. 4,443,946 uses a stylus supported on the fixed member for universal pivotal motion and for longitudinal motion. The pivotal motion causes sliding between the stylus and the cutting tool, which will introduce unknown errors depending on the initial presetting of the tool. Similar errors will occur in the longitudinal direction if the motion of the tool tip is slightly offset from the longitudinal axis of the device. Also, the construction of this type of device is expensive and it requires an excessive amount of space, which is frequently not available.